1. Field of the Invention
The present invention relates to an exhaust turbo-supercharger used in internal combustion engines such as engines of vessels, automobiles, or power generators.
This application is based on Japanese Patent Application No. 2005-306505, the content of which is incorporated herein by reference.
2. Description of Related Art
An exhaust turbo-supercharger forcibly supplies air into a combustion chamber of an internal combustion engine to increase the combustion efficiency, thereby improving the output of the internal combustion engine.
An example of such a known exhaust turbo-supercharger is an exhaust turbine-supercharger including an exhaust turbine unit driven by an exhaust gas and an compressor unit (intake turbine unit) driven by the exhaust turbine unit to send the outside air to a combustion chamber under pressure (see Japanese Unexamined Patent Application Publication No. 2002-70568).
The exhaust turbine unit includes an exhaust turbine housing having a spiral channel therein and an exhaust turbine provided substantially at the center in the radial direction of the exhaust turbine housing. The compressor unit includes an compressor housing having a spiral channel therein and an compressor provided substantially at the center in the radial direction of the compressor housing.
The exhaust turbine and the compressor are concentrically connected with a shaft. A bearing housing is provided between the exhaust turbine housing and the compressor housing. A bearing that rotatably supports the shaft is provided in the bearing housing.
In this exhaust turbo-supercharger, the exhaust turbine is rotationally driven by a flow of exhaust gas introduced into the exhaust turbine housing. Thereby, the compressor connected to the exhaust turbine with the shaft provided therebetween is rotationally driven. Thus, the outside air is sent by the compressor under pressure.
A heat shield component is provided between the exhaust turbine housing and the bearing housing. The heat shield component blocks the transmission of heat therebetween. Accordingly, the heat of the exhaust gas emitted from the exhaust turbine housing is not easily transmitted to the bearing in the bearing housing, thus preventing problems such as bearing seizure.
In the vicinity of the inner wall surface of the spiral channel of the exhaust turbine unit, the flow velocity of the exhaust gas flow is decreased by the frictional resistance against the inner wall surface of the channel (that is, in the exhaust gas flow, a boundary layer in which a velocity defect is generated relative to the main flow velocity is formed in the vicinity of the inner wall surface of the channel).
As a result, distortion is generated in the velocity distribution of the exhaust gas flow supplied to the exhaust turbine, resulting in an increase in impact loss at the entrance of rotor blades. Consequently, the efficiency of the exhaust turbine unit is decreased.